The oil and gas industry is faced with the need to produce more fossil energy or to prove that the production of such energy is possible. Efforts expended heretofore in this regard have, among other things, revealed that a considerable amount of fossil energy may be obtained from shale deposits, which were previously thought to be only barriers to the migration of subterranean hydrocarbons. Rather recently it has been learned that many of the same shales, whose only function was thought to serve as a caprock or impermeable barrier to subterranean hydrocarbon migration, in fact, have served as massive agents to absorb natural gas. This natural gas can be converted to commercial production. Following drilling and fracturing the shale, so much of this type of unconventional gas production has been proven up at this point in time that the supply has exceeded the demand and prices of natural gas have diminished significantly.
Many operators who have paid the cost to drill, such as operators in the Barnett Shale in the area of Fort Worth, North Texas, have shut in their successful shale gas wells because the market price of the gas has fallen below acceptable economic levels for the operation of such wells. Therefore, there is a need to enhance the natural gas market and thereby encourage added drilling aimed at improving the natural gas reserves.
Gas to Liquid (GTL) technology for converting natural gas, which consists primarily of methane, to a liquid fuel has existed for nearly a century. A recent resurgence of interest is providing significant advancements in the rapidly growing art. Prior art teaches that natural gas may be converted to higher molecular weight hydrocarbons by generally two techniques, either a direct transformation with an intermittent step of creating a synthesis gas (syngas) or a gas composed generally of hydrogen and carbon monoxide.
Direct transformation into higher molecular weight hydrocarbons may occur through pyrolysis, during which methane generally at 250° C. to 100° C. is passed through a catalyst in the absence of substantial amounts of oxygen. Processes and catalysts are described in U.S. Pat. Nos. 4,199,533; 4,547,607; 4,704,496; 4,801,762; 5,093,542; 5,157,189; and 5,245,124. These processes require high activation energy and can be difficult to control. As a result, there is minimal commercial use of direct GTL processes.
Two or three GTL processes where the natural gas is first converted to syngas have more prevalent commercial use than the direct processes. For example, Mobil has developed M-gasoline which is created by a three stage process. Natural gas is converted to syngas which is transformed into methanol which is finally made into M-gasoline. However, the most common GTL process is a two stage process in which the natural gas is first converted to syngas which is then changed into liquid hydrocarbons via the Fischer-Tropsch process.